NEW YORK (Reuters Health) - Children born to women who take
acetaminophen during pregnancy may be at increased risk of
attention deficit hyperactivity disorder (ADHD) and similar
behavioral problems, new findings suggest.

The study does not show that prenatal exposure to the
medication causes ADHD, and the increase in risk is small, Dr.
Jorn Olsen, one of the study's authors, told Reuters Health.

Nevertheless, "it's reasonable to say that there's no reason
to use these drugs during pregnancy unless there is a clear
medical indication," said Olsen, a professor of epidemiology at
UCLA and at Aarhus University in Denmark.

Acetaminophen, or paracetamol, has been available over the
counter since the 1950s, Olsen and his colleagues note in their
report in JAMA Pediatrics.

While the medication is widely considered to be safe to use
during pregnancy, they add, recent studies have shown it can
disrupt hormone function in pregnant rats and mice.

Given that hormones play a key role in guiding fetal
development, the researchers decided to investigate whether
acetaminophen exposure might be related to ADHD risk. They
looked at 64,322 children and mothers enrolled in the Danish
National Birth Cohort between 1996 and 2002.

More than half - 56 percent - of mothers reported using
acetaminophen during pregnancy.

Children born to these women were 37 percent more likely to
be diagnosed with hyperkinetic disorder (HKD), a severe form of
ADHD. They were 29 percent more likely to be prescribed ADHD
medications, and 13 percent more likely to exhibit ADHD-like
behaviors at age 7.

The acetaminophen-ADHD link was stronger for women who used
the medication during more than one trimester of pregnancy, and
increased with the frequency of exposure.

Five to six percent of babies born today will develop ADHD
symptoms during their lifetimes, Dr. Olsen noted; based on the
current findings, that risk would increase to about 7 percent
for children exposed to acetaminophen prenatally.

"It's still a modest increase," he said. "For the women that
are taking these drugs there are no special reasons for
concern....for women who are pregnant and who have not taken
these drugs, I think that the take-home message would be a lot
of the use of these particular drugs during pregnancy is not
really necessary."

An editorial accompanying the study pointed out that Olsen's
team adjusted for things that might have also influenced fetal
development, such as the mothers' inflammation or fever, while
possibly explaining why the women took acetaminophen. But the
researchers could not account for every reason the women took
acetaminophen, so more study is needed.

Pregnant women should consult their physician about whether
or not they should be taking acetaminophen during pregnancy, one
of the editorial's coauthors, Dr. Kate Langley, told Reuters
Health.

Even if acetaminophen exposure does turn out to have a
causal relationship with ADHD, she added, it is only one of many
environmental and genetic risk factors involved in the disease,
said Langley, a professor of psychology at Cardiff University
and the MRC Center for Neuropsychiatric Genetics and Genomics.

"In terms of research, it's definitely something that should
be followed up, but it's the first step on a long road to try to
determine how we should interpret these findings," she said.